1. Field of Invention
The present invention relates to a high voltage device and a manufacturing method of a high voltage device; particularly, it relates to such device and manufacturing method wherein the breakdown voltage is increased.
2. Description of Related Art
FIG. 1A shows a cross-section view of a prior art double diffused drain metal oxide semiconductor (DDDMOS) device. As shown in FIG. 1A, the N-type DDDMOS device is formed in a P-type substrate 11, which includes a gate 13, an N-type drain 15, an N-type source 16, and an N-type drift region 18. The drain 15, the source 16, and the drift region 18 are formed by a lithography process and an ion implantation process, wherein the lithography process defines the implantation regions by a photoresist mask together with a self-alignment effect provided by all or part of the gate 13, and the ion implantation implants N-type impurities to the defined regions in the form of accelerated ions. The drain 15 and the source 16 are beneath the gate 13 and at different sides thereof respectively.
FIG. 1B shows a depletion contour map of a prior art DDDMOS device. When a positive voltage is applied to the drain, a depletion region is formed between the N-type drain 15 and the P-type substrate 11. The depletion contour 19a indicates the boundary of the depletion region, wherein the region outside the depletion contour 19a is neutral, and the region inside the depletion contour 19a is depleted. FIGS. 1C and 1D show simulated voltage contour maps when the N-type DDDMOS device is ON and OFF respectively. A higher density of the voltage contours indicates a lower breakdown voltage.
The DDDMOS device is a high voltage device designed for applications requiring higher operation voltages. However, if it is required for the DDDMOS device to be integrated with a low voltage device in one substrate, the high voltage device and the low voltage device should adopt the same manufacturing process steps with the same ion implantation parameters, and thus the flexibility of the ion implantation parameters for the DDDMOS device is limited; as a result, the DDDMOS device will have a lower breakdown voltage and therefore a limited application range. To increase the breakdown voltage of the DDDMOS device, additional manufacturing process steps are required, that is, an additional lithography process and an additional ion implantation process are required in order to provide different ion implantation parameters, but this increases the cost.
In view of above, to overcome the drawbacks in the prior art, the present invention proposes a high voltage device and a manufacturing method thereof which provide a higher breakdown voltage so that the high voltage device may have a broader application range, in which additional manufacturing process steps are not required and the device area is not increased, such that the high voltage device can be integrated with and a low voltage device and manufactured by common manufacturing process steps.